Several pathogenic bacteria decorate their cell surface with sialoglycoconjugates
that in many cases mimic host structures and serve as important
virulence factors. In addition to N-acetyl neuraminic acid, the prevalent sialic acid in the
humans, O-acetylated sialic acids are observed in bacteria that carry acetyl groups at
position C-7, C-8 and/or C-9. The ability to modify cell surface sialo-glycoconjugates
by O-acetylation depends on the presence of sialate O-acetyltransferases, an enzyme
class that catalyzes the transfer of acetyl groups from acetyl Coenzyme A to hydroxyl
groups of either free or CMP-activated sialic acid or particularly sialylated carbohydrate
structures. On the genetic level, distinct mechanisms were observed which lead to an
‘on/off’ switch of sialate O-acetyltransferase expression and/or modification of the
enzymatic activity. The resulting changes in the degree of surface O-acetylation of these
bacteria can lead to a huge structural variety that make them difficult targets for the
immune system. Structural and biochemical analyzes demonstrated that bacterial sialate
O-acetyltransferases evolved independently on two distinct structural frameworks, the
left-handed β-helix fold and the α/β-hydrolase fold.
Keywords: Sialate O-acetyltransferases, lipooligosaccharides, lipopolysaccharides,
capsular polysaccharides, sialate O-acetylation, acetyl coenzyme A, pathogenic
bacteria, O-acetylation.
